YOU have probably hear or read one of Aesop?s fables, though you may not recognize the name. One of his stories, for example, involves a fox who tries unsuccessfully to reach a bunch of grapes and finally gives up, muttering that the grapes probably weren?t that sweet in the first place, an attitude that is now commonly referred to as ?sour graping.?

Another story involves a thirsty crow that comes across a water pitcher that isn?t quite empty. Unable to reach the water deep inside the jar, the crow looks around, spots some stones and starts dropping them into the jar until the water level rises enough for him to drink. The lesson learned: necessity inspires creative solutions.

Some creative thinking

British biologists have now demonstrated that the idea of crows and related birds such as the rook and raven doing some creative thinking to achieve a goal is more than a memorable piece of fiction. Working with four rooks raised in captivity, Christopher David Bird from the University of Cambridge and Nathan John Emery from the Queen Mary University of London gained evidence of these corvids using tools to retrieve a worm from a partially filled container of water.

Bird and Emery have posted several short videos of their work with the rooks on YouTube. All of them start the same way: a water-filled tube is placed inside a cage that holds a rook. When the black bird examines the tube, it sees a worm made of wax floating on the water and reaches in to grab it with its beak. Unfortunately, while the tube just big enough to stick his head in, the water level is lower than its beak can reach.

The bird stares at the tube of water for a while then steps aside as a handful of stones is placed on the plastic base to which the tube is glued. The bird goes back to examining the tube, then eyes the stones. Alternately checking the water level from the side and peering into the tube to make sure the plan is working, the crow drops just enough stones so it can reach in and grab the worm. Once this is done, the plastic setup is removed from the cage and the video ends.

There are a few variations to the exercise. Sometimes the stones are of different sizes and the rooks figure out that the bigger stones help them retrieve the worm faster. In another instance, rooks learned that water has unique properties compared to sand, which led to their decision to focus on placing rocks only into the water-filled tube to retrieve the worm.

First empirical evidence

?The results of these experiments provide the first empirical evidence that a species of corvid is capable of the remarkable problem-solving ability described more than two thousand years ago by Aesop,? Bird and Emery wrote in their paper. ?What was once thought to be a fictional account of the solution by a bird appears to have been based on a cognitive reality.?

The rooks in the British study aren?t the first animals to demonstrate an ability to use tools. For example, New Caledonian crows, another relative of the rook, have bent straight wires into hooks to reach food. Chimpanzees have long been known to use stones to crack open nuts and collect sticks to fish for termites in their mounds. Dolphins use sponges to find prey hidden under the sand. And elephants can fashion tree bark into water canteens.

What Bird and Emery found interesting is that the rooks in the wild don?t use tools. They suggested that unlike the captive birds, the wild rooks tend to rely on easily accessible food sources and so didn?t need to develop these skills. Necessity, as Aesop put it so many years ago, may really be the mother of invention.

The study was published online August 7 and will be printed later this month in an issue of the journal Current Biology.

E-mail the author at massie@massie.com.